1. Field of the invention
This invention relates to an apparatus and method for applying adhesive to the edges of a slit formed in a resilient tubular body. More particularly, this invention relates to an apparatus and method for applying glue or adhesive to the edges of slit tubular pipe insulation.
2. Description of the Prior Art
Pipe insulation is usually formed as a tubular body from a foamed polymeric material, such as polyethylene. The pipe insulation is formed in an extrusion process wherein a blowing agent is injected or pumped into an extruder under high pressure and mixed with the polymeric material to be extruded. The polymeric material is then passed through a die head. As the polymeric material passes through the die head, the reduction in pressure causes the blowing agent to expand within the polymeric material to produce the cells of the foam.
Once the pipe insulation has been extruded, it is cut into initial lengths for further processing and stored for a period of time to cure, allowing the blowing agent within the cells of the foam to diffuse and be replaced with air. After the pipe insulation is cured it can be processed further. This typically involves providing the pipe insulation with a longitudinal slit which allows the pipe insulation to be easily positioned around a length of pipe to be insulated. Glue or adhesive is also applied to the edges of the slit so that the edges can be secured together once the pipe insulation is installed around the pipe.
The longitudinal slit is formed by feeding the lengths of pipe insulation, one at a time, to a slitter which is provided with a blade or cutting element which cuts through the wall of the pipe insulation. Puller belts used to feed the insulation through the slitter are also used to deform the pipe insulation by squeezing the walls of the insulation together. The deformation of the pipe insulation by the puller belts causes the edges of the slit to be spread apart after it is formed. A plow further flattens the edges of the slit so that the edges lie in a single plane 180.degree. apart. A pressure sensitive adhesive is then applied to the edges of the slit. This may be accomplished by applying the adhesive to a single strip of polyester tape, such as Mylar, which is then placed over the edges of the slit so that the adhesive is applied to the edges. The pipe insulation is then allowed to spring back to its original shape wherein the tape strip is folded over on itself between the edges of the slit with the edges of the slit facing one another. The tape acts as a release liner which prevents the edges from sticking together before use. After the slit is formed and adhesive has been applied to the edges as described above, the pipe insulation may then be cut again into appropriate lengths for packaging and shipment to the end user.
Due to the extreme deformation that the pipe insulation undergoes in the prior art methods of forming the slit and applying adhesive, further processing of the pipe insulation in this manner immediately after it is extruded usually results in damage to the pipe insulation caused by the collapsing or rupturing of the foam cells. Thus it is essential that the pipe insulation be allowed to cool and cure after it is extruded. While the cured foam undergoes less damage, it takes longer to process and requires numerous handling steps.
What is needed is a means for applying adhesive to the edges of the slit of tubular pipe insulation which does not crush or deform the pipe insulation to a significant degree and which can be used immediately after the pipe insulation has been extruded and prior to curing so that the insulation can be cut to length for packaging and shipment.